Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and particularly relates to a technique of appropriately correcting inclination of an image on a printed matter.
Description of the Related Art
In generating a printed matter by printing a text and an image (hereinafter, “image”) on a sheet, there is a known technique of adjusting an image position to be printed on a proper position of the sheet.
Techniques to adjust the image position include a method of mechanically adjusting the positions of the sheet and a print head, and a method of adjusting the main scan print speed and the sub scan direction density by adjusting the sheet conveyance speed and the polygon mirror rotation speed.
In recent years, in addition to these methods, there is a technique used in some cases to adjust the image position and inclination by deforming image information before printing in a direction of canceling an image position shift and image distortion at printing. At double-sided printing, in a case where inclination (skew) exists on each of images on front/back of the sheet, this technique can typically execute position adjustment easily for each of the front/back by deforming the image so as to direct opposite directions.
Related techniques are described in the related arts such as JP 2006-82469 A and JP 2000-244728 A. Hereinafter, problems will be described together with JP 2006-82469 A and JP 2000-244728 A.
While the above-described image position adjustment involving image deformation (skew correction) is capable of highly flexible image position adjustment, it involves the following problems.
[Problem 1] Difficulty in Appropriately Setting Correction Target Position
Important factors for image position adjustment include position shift adjustment of front/back of the sheet (front/back registration).
In usual cases, position adjustment is executed so as to adjust a back surface to be fitted to a front surface on the assumption that the position adjustment has been applied for the front surface. In a case, however, where the front surface has not been printed at a desirable position, the printing position turns out to be undesirable in some cases even when the front/back registration is suitably fitted.
For example, there is an assumed case where the sheet having distortion is scheduled to be cut into a predetermined size after printing. In this case, the sheet is cut using a trim mark for cutting, namely, a predetermined cutting mark, as a guide. As a result, it is possible to obtain a printed matter having uniform image positions and the sheet size. However, in a case where the positional relationship between the print sheet before cutting and the trim mark for cutting is not properly maintained, particularly in a case where parallelism between the trim marks for initial cutting and the sheet side being abutted against a position adjustment tool at cutting is not properly maintained, a great amount of labor would be needed for post processing. In another case where cutting is not assumed, it would be preferable that adjustment is performed to achieve an image position that has no inclination in average toward each of the sides of the sheet, not a specific side.
While the above description assumes a case where there is distortion on an outer form of a sheet, this assumption applies not only to a case where a non-professional user creates an irregular-sized sheet by cutting a large-sized original sheet, but also to a case of various types of regular-sized sheets supplied from professionals. The reason is that even a cut sheet cut into a predetermined regular size by a professional machine usually includes a slight cutting error and a shift in right-angles at four corners, and that in some cases, storage condition after cutting would cause irregular expansion/shrinkage and this would decrease rectangularity at four corners.
JP 2006-82469 A describes a means for setting skew with respect to a predetermined end-side portion of the sheet, specifically, a configuration capable of adjusting the distortion appropriately by the user operation while viewing the image. In this, however, a correction target depends on experience and sensitivity on the user. Therefore, this technique cannot be easily utilized by workers having little experience in printing operation, except professionals.
[Problem 2] Necessity to Provide Margins in Image Print Region
The above-described technique of adjusting the image position and inclination by deforming image information can be achieved by obtaining a printable image region larger than a print image main body and then by performing deformation and position adjustment of the image within the region. The difference between the print image main body and the printable image region is referred to as a “margin”.
While the maximum amount of adjustable image position depends on the size of the margin, enlarging the margin would be a factor of problems such as an increase in the cost of image forming apparatus, overall enlargement of the apparatus, and decrease in printing productivity. Therefore, enlarging the margin has its limit.
The above-described JP 2000-244728 A relates to document inclination correction processing at image reading. While printing in the present application and reading in JP 2000-244728 A differs n usage and objects, those have a common issue in that image deformation processing needs a margin and that size of the margin has a limitation. JP 2000-244728 A describes a technique of issuing an alert indication and modifying correction, or the like, when inclination of the document exceeds a maximum correction angle. There is, however, there is no suggestion of effectively using the limited margin.
[Problem 3] Possibility of Image Quality Deterioration in Skew Correction
Image position adjustment using image deformation involves processing of deforming a printed image, and thus, might involve image quality deterioration that is visually recognizable. In order to cope with this case where image quality deterioration is undesirable, it would be possible to prepare a switch to avoid executing skew position adjustment. In this case, however, simply selecting to avoid executing a skew correction amount alone might cause a shift of the image position with respect to the sheet in an unintended direction. In order to cope with this, it is necessary to provide countermeasures such as retrying image position adjustment and preliminarily executing individual adjustments with execute/not execute of skew position adjustment, causing lots of trouble.